1. Field of the Invention
The present invention relates to cleaning devices for the wire electrodes of corona dischargers, for example, to a device for cleaning the wire electrode of a corona discharger for use in electrophotographic image forming apparatus.
2. Description of the Related Art
Corona dischargers comprising a discharging wire provided inside a box-shaped shield case longitudinally thereof are usually used in copying machines and printers adapted to practice an electrophotographic process. The corona discharger serves as a charger for sensitizing the surface of a photosensitive member or as a transfer charger for transferring toner images formed on the photosensitive member to copy paper.
Usually, a high voltage of one thousand, several hundred volts to thousands of volts is applied to the discharger to effect corona discharge to give a uniform charge to the surface of the photosensitive member or copy paper.
However, when the corona discharger is used for a long period of time, silica or toner particles adhere to the wire to result in altered discharging characteristics, so that the discharger fails to charge the photosensitive member or copy paper efficiently and uniformly.
Especially when the discharger is used as a sensitizing charger, variations in the photosensitive member charging characteristics entail varying image densities, while uneven charging produces irregularities, spots and the like in copy images.
To preclude such adverse effects, it has been conventional practice for the serviceman to remove the adhering particles from the wire by periodic cleaning. The corona discharger therefore requires much labor and a substantial cost for maintenance.
Devices for automatically cleaning the wire are available which comprise a cleaning member (cleaner pad) disposed inside the corona discharger and reciprocatingly movable by the rotation of a motor through a pulley and a drive rope. Such a device is disclosed, for example, in Japanese Laid-Open Patent Application No. 53-106054.
However, the conventional wire cleaning device is not always operable with good stability since the drive force is frictionally transmitted from the pulley to the drive rope. Depending on the state of contact between the pulley and the rope, tautness of the drive rope or the condition of the cleaning member as a load, the pulley, if rotated, fails to move the rope with the rotation owing to slippage therebetween. Troubles are therefore likely to occur; the cleaning member will fail to start traveling from its standby position (home position) or will stop during travel.
Further depending on the state of contact between the pulley and the drive rope, the tension on the rope, the condition under which the cleaning member as a load is held, and the surface state of the wire, the motor will be subjected to an excessive loading torque greater than its output, consequently failing to start up or coming to a halt during rotation. Accordingly, the above-mentioned unstable factors are likely to entail the trouble that the cleaning member is unable to start traveling from the home position or comes to a stop during travel.
The cleaning member is heavily loaded by coming into contact with a member provided at the end of range of its travel, whereby the drive force transmitting portion is brought into a locked state. The above trouble is therefore very likely to occur since an especially great drive force is needed to unlock the transmitting portion and release the cleaning member from the end member.
Furthermore, the use of the corona discharger in an apparatus for practicing the electrophotographic process imposes great limitations on its size and configuration, with the result that it is dimensionally difficult to provide drive means which is operable free of an excessive load.
If the above-mentioned trouble occurs, the corona discharger can not be used for the contemplated purpose, and there arises a need for the serviceman to repair the cleaning device. This reduces the operation efficiency of the copying machine or printer incorporating the discharger.
With the wire cleaning device disclosed in the aforementioned publication, the cleaning member is merely formed with a bore for passing the wire therethrough and is accordingly low in the pressure of contact with the wire. Thus, there is a likelihood that the wire will not be fully cleaned.
The device has another problem. The cleaning device, which is in contact with the wire even at the home position, impairs the wire positioning precision, exerts an adverse influence on the discharging characteristics of the wire and deteriorates early by being affected by corona discharge.
In view of the above problem, Japanese Laid-Open Utility Model Application No. 61-153052 discloses a device which comprises a pair of cleaning members movable along a corona wire while holding the wire therebetween to clean the wire.
With this device, the pair of cleaning members are biased into holding contact with the wire by a spring during movement and adapted to come into engagement with an engaging member on the discharger casing to release the wire upon reaching the end of the wire.
Nevertheless, the device has the problem of being complex in construction because the spring is used for pressing the cleaning members into contact with the corona wire and being large sized because the spring must be powerful to give a high contact pressure. The device has another problem in that the spring fatigues during a long period of use to give a lower contact pressure.